306 



Dr. T. Goodey. Further Observations on 

 Bacteria in Millions per Gramme. 







After 

 17 days. 



After 

 50 days. 



After 

 85 days. 



After 

 126 days. 



After 

 162 days. 



TJ 



30 



16 



20 



12 



12 



12 



H 



2-7 



65 



75 



120 



96 



70 







86 



138 



ys 



78 



58 



o 80 

 % 60 

 .E 40 

 ■f 20 



/ 



/ - 

 / •' 



/ : 

 I / 



1/ 



Untreated 



1513 



50 



85 



Days 

 Fig. 3. 



162 



especially, at this point, the figures for the Amceba Umax. These are the 

 same as those for Amceba Umax in the earlier experiment, where 30,000 

 were present at 43 days, when the drop occurred in the numbers of bacteria. 

 The result of the second experiment fully confirms that of the first, and 

 points conclusively to the fact that the activity of the protozoa has had a 

 depressing effect upon the numbers of bacteria. A further point brought out 

 is that the limiting action of protozoa is chiefly operative through the 

 activity of a small Amceba Umax, and that for this particular soil, at any 

 rate, we can say that the necessary number of this amoeba to produce the 

 effect is about 30,000 per gramme. 



In the earlier experiment the depressing effect occurred at 43 days, and in 

 the confirmatory experiment at 85 days, which is 42 days longer. It is not 

 difficult, however, to suggest an explanation of this. If we refer to the 

 number of Amceba Umax present at the beginning of the experiment we 

 shall see that in the first case (T + 5 per cent. U) there were about 600 per 

 gramme, whilst in the second case (H + 5 per cent. U) there were about 150 

 per gramme. Thus there was a much greater initial number in the one case 

 than in the other, and consequently a shorter time would be necessary for 

 them to multiply and reach the figure at which they would have the 

 depressing effect upon bacterial numbers. Moreover, in the treated portion 

 of the (T + 5 per cent. U) soil all the amoeba had not been killed off as in 

 the treated portion of the (H + 5 per cent. U), and these remaining forms, 



